To cite UCSCXenaTools in publications use:

  Wang et al., (2019). The UCSCXenaTools R package: a toolkit for
  accessing genomics data from UCSC Xena platform, from cancer
  multi-omics to single-cell RNA-seq. Journal of Open Source Software,
  4(40), 1627, https://doi.org/10.21105/joss.01627

A BibTeX entry for LaTeX users is

  @Article{,
    title = {The UCSCXenaTools R package: a toolkit for accessing genomics data from UCSC Xena platform, from cancer multi-omics to single-cell RNA-seq},
    author = {Shixiang Wang and Xuesong Liu},
    journal = {Journal of Open Source Software},
    year = {2019},
    url = {https://doi.org/10.21105/joss.01627},
  }